I am having almost identical problems to the OP. I can ssh into my box, I can ping and sucessfuly resolve domain names to IP addresses but as far as web browsing, apt-get, wget or FTP are concerned nothing works, they all just timeout. I don't have any IPtable firewall stuff setup and when I make the box a DMZ host on my hardware firewall the problem still exists.

Any help what-so-ever would be gratefully received, please bare in mind that I am a novice Linux user - I am using a hybrid version of Knoppix called Knoppmyth which is designed for tivo style boxes.